1. Field of the Invention
The invention relates generally to electrical switching apparatus and, more particularly, to vented cases for electrical switching apparatus.
2. Background Information
Electrical equipment such as, for example, relays, circuit breakers, electric meters and transformers, are typically housed within an electrical enclosure such as, for example, a housing such as a cabinet.
Panelboards or load centers, for example, are types of electrical enclosures which serve to distribute power for residential or commercial applications. Typically, the panelboard or load center includes a housing enclosing a plurality of electrical switching apparatus (e.g., without limitation, circuit breakers) for protecting branch circuits against electrical faults or overload conditions. It is desirable to maximize the efficiency with which the available space within the housing is used. Accordingly, the circuit breakers are often disposed, for example, adjacent one another in parallel rows with one or more bus bars extending between the rows. The circuit breakers may also be removably coupled to a DIN rail. DIN is short for Deutsches Insitut für Normung eV, which is a German standard-setting organization. Accordingly, a DIN rail is a connecting rail structure which is designed to satisfy DIN standards. Some manufacturers of circuit breakers provide the circuit breaker with a DIN rail mounting structure, such as an integrally molded recess sized to provide snap-on attachment to the DIN rail.
FIG. 1 shows an example of three such circuit breakers 2, which are ganged (e.g., coupled) together side-by-side. Each circuit breaker 2 is essentially identical, including a case 6 with a first half 8 and a second half 10. Handles 12 protrude from the top (from the perspective of FIG. 1) of the cases 6 and, in the example of FIG. 1, are ganged (e.g., coupled) together. The end 4 of each circuit breaker 2 includes a terminal 14, with protrusions 16,18 being disposed on opposite sides of the terminals 14. A single vent 20 provides the sole means for ventilating ionized gases from within each circuit breaker 2. The interior of the second half 10 of one of the circuit breakers 2, and the terminal 14, protrusion 18 and vent 20 thereof are shown in FIG. 2, which also shows the aforementioned molded DIN rail mounting structure 22.
Such circuit breakers 2 are subject to industry safety regulations. For example and without limitation, the Underwriter's Laboratory (UL) establishes regulations pertaining to the specifications of circuit breaker arc chutes (not shown) and, in particular, the venting capability of circuit breakers to sufficiently vent ionized gases which are produced as a byproduct of an arc generated when the circuit breaker trips. Such regulations are becoming increasingly stringent. As a result, many existing circuit breakers such as, for example, the circuit breaker 2 with single vent 20 discussed hereinabove with respect to FIGS. 1 and 2, do not satisfy such regulations for use in certain applications (e.g., without limitation, branch circuit protection). It is, therefore, difficult to simultaneously satisfy both the established industry safety regulations and the design objective of minimizing the overall size of the circuit breakers, and thus the overall space required for the panelboard or load center.
There is, therefore, room for improvement in electrical switching apparatus and in cases therefor.